In a 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)/LTE-A (LTE-advanced) system, a downlink multiple access mode generally used is an orthogonal frequency division multiple access (OFDMA) mode. In terms of time, downlink resources of the system are divided into orthogonal frequency division multiplexing (OFDM) symbols, and in terms of frequency, the downlink resources of the system are divided into subcarriers.
In LTE release 8, LTE release 9 and LTE release 10, one downlink subframe includes two timeslots, and each timeslot includes 7 or 6 OFDM symbols, so that a downlink subframe includes 14 or 12 OFDM symbols. One physical resource block (PRB) includes 12 subcarriers in a frequency domain, and one timeslot in a time domain, which means that one PRB includes 7 or 6 OFDM symbols. A subcarrier in an OFDM symbol is called a resource element (RE), and therefore one PRB includes 84 or 72 REs. In one subframe, two PRBs of two timeslots at a same frequency position are called a physical resource block pair; and in LTE, a resource granularity of downlink transmission is a physical resource block (PRB) pair.
In LTE release 10 and earlier LTE systems, a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) are time-division multiplexed in one subframe. The PDCCH is borne on the first n symbols of a subframe, and downlink data that the PDCCH schedules is mapped from the (n+1)th symbol of the subframe. In one subframe, all PDCCHs scheduling user equipments (UEs) are multiplexed together, and are then sent in a PDCCH area. One PDCCH may be formed by 1, 2, 4 or 8 control channel elements (CCEs); one CCE is formed by 9 resource element groups (REGs); and one REG occupies 4 REs.
In LTE release 10 and earlier LTE systems, according to an index of the first CCE of a downlink grant (DL_grant) for scheduling a UE, that is, a start position of an enhanced physical downlink control channel (E-PDCCH), a physical uplink control channel (PUCCH) format 1a/1b channel may be determined in an implicit manner to bear acknowledgement/negative-acknowledgement (ACK/NACK) feedback information for downlink data transmission.
As control information in a PDCCH is obtained by means of convolutional encoding with master code being 1/3 and circular buffering based rate matching, when an encoding rate is less than 1/3, it may occur that different CCEs include a same modulation symbol. For example, when the PDCCH is formed by 4 CCEs, each including 72 bits, the PDCCH can carry totally 288 encoded bits. Assuming that the PDCCH originally has 48 bits, the bit number becomes 144 after the 1/3 encoding, and becomes 288 after the circular buffering based rate matching, which is equivalent to a repetition encoding; and the 288 bits are finally mapped to the four CCEs of the PDCCH. Therefore, modulation symbols in the third CCE and the fourth CCE are completely the same as modulation symbols in the first CCE and the second CCE.
Under the foregoing situation, a base station sends a PDCCH at aggregation level (AL) 4, but when performing blind detection, a UE may possibly detect information in the third CCE and the fourth CCE as a PDCCH at aggregation level 2. Therefore, the UE may determine a PUCCH format 1a/1b channel in an implicit manner according to an index of the first CCE of the PDCCH at aggregation level 2, that is, an index of the third CCE. However, the base station may regard that the PUCCH format 1a/1b channel allocated to the UE is determined by the first CCE, so that feedback information cannot be correctly transmitted. It can be seen that unclearness of the CCE detection (that is, incorrect judgment on the start position of the E-PDCCH) will lead to unclearness of the PUCCH format 1a/1b channel determined by the UE.
In a LTE system later than release 10, with introduction of a multi-user multi-input multi-output (MIMO) antenna system and coordinated multi-point (CoMP) transmission and like technologies, a control channel capacity is restricted. Therefore, a PDCCH, which is transmitted based on a MIMO pre-coding mode is introduced and the PDCCH can be demodulated based on a UE-specific reference signal, that is, a demodulation reference signal (DMRS), and the PDCCH here is also called an E-PDCCH. An E-PDCCH is not in a control area of the first n symbols of a subframe, but is in a downlink data transmission area of the subframe. E-PDCCH is frequency-division multiplexed with a PDSCH, and may occupy a different PRB pair from that occupied by the PDSCH. Alternatively, an E-PDCCH and a PDSCH may be multiplexed in a same PRB pair. In addition, a group of PRB pairs for E-PDCCH(s) may be configured for a cell, so that each UE in the cell knows all the PRB pairs for E-PDCCH(s) that are configured by a base station. Or, a PRB pair for E-PDCCH transmission may be configured for each UE, which means that PRB pairs for E-PDCCHs that different UEs need to detect may be different.
Using LTE release 11 as an example, a reference signal of an E-PDCCH is a UE-specific reference signal, and can support 4 ports (that is, DMRS ports 7, 8, 9 and 10 for PDSCH demodulation in LTE release 10). A data part of an E-PDCCH is used to bear modulation symbols of control information after coding and modulation.
An E-PDCCH CCE, hereinafter called an eCCE, is also defined in LTE release 11. Using a localized E-PDCCH as an example, there are many REs that can be used to transmit an E-PDCCH in a PRB pair, and these REs may further be divided into several eCCEs. An E-PDCCH is formed by one or more eCCEs by means of aggregation, and needs to be blindly detected by a UE. As control information in the E-PDCCH is also obtained by means of convolutional encoding with master code being 1/3 and circular buffering based rate matching, a problem also exists that a UE judges a start position of the E-PDCCH incorrectly.